1. Field of the Invention
The present invention generally relates to a fine adjustment mechanism, in particular, to a fine adjustment mechanism for carrying optical elements.
2. Description of Related Art
Along with the progress of the modern video technology, an optical projection device has been broadly used in various situations, such as playing a home theater, presentations of a small meeting and workroom discussions. The optical projection device includes an optical engine and a projection lens, wherein the optical engine is for providing an image light beam, while the projection lens is for projecting the image light beam onto a screen to get imaging. Further, the optical engine usually includes a light source, a light integration rod module (LIR module) and a light valve, wherein the light source is for producing a light beam, the LIR module is for homogenizing the light beam and the light valve is for converting the light beam into an image light beam. In general speaking, the homogenized extent of a light beam depends on the relative position between the light beam and a light integration rod (LIR) where the light beam passes through. Therefore, the LIR module is usually equipped with an adjustment unit for adjusting the incidence position of the light beam where the light beam incident into the condenser lens after passing the LIR so as to make the light beam outgoing from the LIR more homogenous.
Referring to FIGS. 1A and 1B, a conventional LIR module 100 includes a LIR 110 and a holder 120. The LIR 110 has a light incident end 112 and a light outgoing end 114 and is fixed in the holder 120 to avoid the LIR 110 from cracking by an external force. The holder 120 includes a alignment element 122, and an optical engine housing 200 has a first raised rib 202a, a second raised rib 202b and a through hole 204. As the LIR module 100 is assembled on the optical engine housing 200, the LIR module 100 is placed on the first raised rib 202a and the second raised rib 202b, and the alignment element 122 is inserted into the through hole 204, wherein the axial displacement in Z direction of the LIR module 100 is restricted by a mutual latching between the alignment element 122 and the through hole 204. Thereafter referring to FIG. 1C, a fixing sheet 212 with four elastic sheets 212a is used to cover the LIR module 100, and by fastening the fixing sheet 212 with four screws 214, the LIR module 100 is fixed on the optical engine housing 200. Herein the first raised rib 202a, the second raised rib 202b and the elastic sheet 212a surround the LIR module 100 and are flat-fittingly in close contact with the LIR module 100, so as to restrict the axial displacements of the LIR module 100 in X direction and Y direction.
Referring to FIGS. 1C and 1D, a first adjusting screw 222 and a second adjusting screw 224 are respectively disposed at the adjacent two sides of the optical engine housing 200 and are adjacent to the light outgoing end 114 of the LIR 110, while a condenser lens 250 is disposed outside the light outgoing end 114. Referring to FIG. 1E, when the center of the light outgoing end 114 departs from the center of the condenser lens 250, the realignment between the center of the light outgoing end 114 and the center of the condenser lens 250 can be achieved by adjusting the first adjusting screw 222 and the second adjusting screw 224. However, during a user turns the first adjusting screw 222 and the second adjusting screw 224, the LIR module 100 may get a rotation of θ around the second raised rib 202b which is served as a pilot at the time. Meanwhile, the light incident end 112 of the LIR 110 in the LIR module 100 would have an offset amount d and the light outgoing end 114 thereof would be lifted from the first raised rib 202a. The offset of the light incident end 112 makes the light beam from the light source fail to be accurately incident at the predetermined position of the light incident end 112 of the LIR 110, which causes a light energy loss after the light beam enters the LIR 110 and moreover affects the evenness of the light beam projected onto a digital micromirror device (DMD).